08 Sienna climate control problems

mrl1004

Help! I have a 2008 Toyota sienna XLE and just recently I have been unable to change the heating/cooling zones. For instance I can't change it to defrost even if I press the defrost button. Right now it is stuck on vents. It's all electronic controls on my model and even if the display is showing feet or defrost it is still coming from the vents. I live in New Hampshire and on cold snowy days I've got to be able to change which zone I want heat. I can't seem to find anyone who has had a similar issue with their vehicle. Ideas? I really don't want to take it to a dealer and get robbed there.

thecardoc3

Being all electronic diagnostics start with a fully functional scan tool. Top independents have invested in tooling that allows them to diagnose and service systems like this right alongside the dealerships. When the Toyota Techstream scan tool was first released the price tag for the shop was almost $10,000, and that's not including the yearly updates. There is now a version of the tool, the Techstream lite that is a little less than half of the full version but requires the shop to invest in some other tools to make it work and then buy short term subscriptions on an as needed basis, and that pretty much sums up your options. Some aftermarket professional level tools might claim to support the system but they will often be limited to pulling and clearing codes if possible. Meanwhile the system supports scan data, bi-direction controls and retraining functions.

If you really want to do this yourself, then you are likely faced with buying a full professional level scan tool that correctly supports the system. Or you can seek out a top independent shop, see the dealer, or resort to throwing parts at this and hope you get lucky. Without at least pulling codes you cant reliably get to first base with this.

fibber2

If you are handy and willing to do some work under the dash, you can go a long way towards diagnosing and possibly fixing this issue yourself. While the XLE has split temperature dampers, the Mode Damper (MD) is common to both sides. The MD outputs air to floor, vents or defroster. The electronic dash controls (selectors and AC Amplifier) send a signal to a servo motor that is supposed to move the flaps to a certain position depending on your selection. The servomotor is located above the gas pedal behind a plastic foot guard, but it's a bit high up and will take some dexterity to reach and remove. The idea here would be to see if the damper is stuck and can't move (broken component within the HVAC box), the motor and it's electronic positioner verification system has failed (most likely, as others have had issue with this component), or if there is no valid signal from the dash controls.

I can't argue with Cardoc's assessment, as the full auto system in your van does have a diagnostic mode that might help better pinpoint the fault. When you push a mode button on the dash, a voltage is sent to the motor that makes it move. A feedback variable resistor (voltage divider) on the motor sends a signal back to the AC Amp telling the controls where in it's travel the motor is based on the voltage drop. It's somewhat crude, but it works. If the internal check mode doesn't see the feedback change with applied motor voltage, it should flag it as a fail.

The question is whether you are willing to pull the motor out to bench test it, verify the mechanical motions of the HVAC box internal flaps, and to monitor the applied motor and feedback voltage sent from the dash controller to determine what might need replacing.